Microelectromechanical system (MEMS) sensor devices often present packaging challenges. For instance, MEMS sensors are typically sealed to perform properly over time. The sealing provides protection from corrosive elements and other harsh operating environments, such as, for example, those presented in an automotive application. The sealing also helps ensure relatively high reliability over the lifetime of the device. For example, with some types of MEMS accelerometers, it is desirable to seal the MEMS accelerometer in a chamber to prevent contamination of the moving parts of the MEMS accelerometer during subsequent processes. In another example, micro-gyroscopes are packaged in a hermetically sealed cavity or enclosure to operate at a known pressure level, typically a pressure level near vacuum, e.g., less than 0.5 torr. Additional packaging challenges arise when the sealed cavity for the MEMS sensor is assembled with an integrated circuit, such as an application-specific integrated circuit (ASIC), designed to control and communicate with the MEMS sensor.
Combining different types of MEMS sensors together on a single die can present further challenges. One combination involves MEMS accelerometers and MEMS gyroscopes. MEMS accelerometer performance improves with damping from gas in the cavity, whereas the MEMS gyroscope operates best undamped. The operating environment of a MEMS accelerometer is accordingly at a much higher pressure level, e.g., near atmospheric pressure, than the near vacuum levels for the MEMS gyroscope. So using a common pressure for the accelerometer and gyroscope devices thus presents performance and/or design tradeoffs. The alternative, providing dual pressures in a single die, presents a considerable technical challenge.